The present invention relates to a method for the thermochemical production of hydrogen from water.
Establishment of a method for producing hydrogen by thermally decomposing water at temperatures below 1000.degree. C, preferably below 800.degree. C, and using as the heat source solar heat or heat from an atomic pile and as the medium such compounds as are available abundantly from the standpoint of natural resources is an important task to be fulfilled as soon as possible in view of the unavoidable exhaustion of fossil fuel and the consequent necessity for securing the source of secondary energy to take its place.
In the circumstances described above, there have heretofore been proposed 60-odd reaction cycles for the production of hydrogen by thermochemical decomposition of water.
Argonne National Laboratory, for example, has proposed a reaction cycle consisting of the following three steps: EQU LiNO.sub.2 + I.sub.2 + H.sub.2 O .fwdarw. LiNO.sub.3 + 2HI 1. EQU 2HI .fwdarw. H.sub.2 + I.sub.2 2. EQU LiNO.sub.3 .fwdarw. LiNO.sub.2 + 1/2O.sub.2 3.
This reaction cycle has not yet been developed to the extent of commercial application, because the reaction of Formula (1) proceeds slowly and the reaction of Formula (3) may possibly produce LiO.sub.2, a highly corrosive compound, under certain reaction conditions.
Euratom has proposed a reaction cycle which consists of the following three steps: EQU 6FeCl.sub.2 + 8H.sub.2 O .fwdarw. 2Fe.sub.3 O.sub.4 + 12HCl + 2H.sub.2 1. EQU 2Fe.sub.3 O.sub.4 + 3Cl.sub.2 + 12HCl .fwdarw. 6FeCl.sub.3 + 6H.sub.2 O + O.sub.2 2. EQU 6FeCl.sub.3 .fwdarw. 6FeCl.sub.2 + Cl.sub.2 3.
An experiment has shown that the reaction of Formula (2) in this reaction cycle does not result in any discernible generation of oxygen, indicating it difficult to have the reaction proceed through the cycle represented by these formulas. The reaction of Formula (3) is problematic in terms of process and heat balance because the heat of sublimation of FeCl.sub.3 is great and, worse still, the ratio of decomposition is small.
As described above, the reaction cycles proposed to date invariably entail problems of some sort or other and, in their existing status, are difficult of commercial application.
An object of the present invention is to provide a method for producing hydrogen by allowing water to be thermally decomposed efficiently at temperatures of not more than 800.degree. C through a combination of commercially quite feasible elementary reactions by using, as the medium, elements or compounds which are available abundantly in nature and which do not exhibit much toxicity and corrosiveness.